Internal combustion engines can be fueled solely by a liquid fuel or, in the case of dual fuel engines, by both a gaseous and liquid fuel. Although the present methods are equally applicable to engines fueled solely by liquid fuel, the present methods will be discussed and explained primarily in the context of a dual fuel engine.
A dual fuel engine can typically operate in two modes, namely, a dual fuel mode (gaseous fuel and liquid fuel) and a liquid fuel mode. In a strictly liquid fuel mode, a liquid fuel, such as diesel fuel, is injected directly into an engine cylinder or a precombustion chamber as the sole source of fuel and energy during combustion. In a dual fuel mode, a gaseous fuel, such as natural gas, is controllably released into an air intake port of the particular cylinder where the gaseous fuel is mixed with air. After a predetermined period of time, a small amount or pilot amount of diesel fuel is injected directly into the cylinder or precombustion chamber in order to ignite the mixture of air and gaseous fuel. Compression of the air/fuel mixture during the compression stroke ignites the liquid fuel which in turn ignites the air/gaseous fuel mixture.
In an internal combustion engine, it is sometimes assumed that the air/fuel mixture to each cylinder is homogeneous. In actuality, of course, the air/fuel mixture to each cylinder is non-homogeneous due to many factors such as variations in manufacturing as well as differences in the operating characteristics of the injectors and/or valves used to control fuel delivery to each individual cylinder. If the control signals used to deliver fuel to different cylinders are of the same duration, such variations can result in different air/fuel ratios within different cylinders.
Detonation is an unacceptable increase in the rate of cylinder pressure and typically occurs when the air/fuel mixture in a particular cylinder is too rich for the current engine operating conditions. Detonation above a predetermined threshold level can cause damage to the cylinder walls, piston, piston rings, valves and other components associated with each individual cylinder. Generally, detonation can be controlled by monitoring and adjusting the air/fuel mixture to each respective cylinder.
It is therefore desirable to control and adjust the air/fuel mixture to each cylinder such that the air/fuel ratio associated with each cylinder will be substantially similar. It is also desirable to reduce the frequency of detonation occurring in any particular cylinder. This can likewise be achieved by controlling and adjusting the air/fuel ratio to each cylinder. Still further, it is likewise desirable to improve fuel economy and reduce emissions.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.